Ultrasonic instrument

ABSTRACT

An ultrasonic invasive instrument such as a biopsy needle has an ultrasonic transducer mounted at one end, with the transducer being electrically coupled to two conductors such as a stylet and central cannula forming the instrument body and transmitting signals from the transducer identifying the instrument&#39;s location in a field transmitted by an imaging scanner, the transducer being coupled to at least one of the conductors by an ohmic or capacitive coupling, with for example body fluids serving as the couplant material.

INTRODUCTION AND BACKGROUND

The present invention relates to an ultrasonic instrument for use ininterventional procedures employed in surgical and medicalinvestigations, treatment or diagnosis, in research and in relatedfields.

In procedures involving the insertion of an instrument into a human oranimal body, it is often necessary for the position of the instrument tobe known accurately. The use of ultrasonic instruments, in particularimaging scanners, to guide the insertion of surgical instruments such aspuncture needles or catheters during invasive medical procedures isknown. The imaging system usually relies on detection of passive echosfrom the instruments, but more recently techniques have been developedin which an ultrasonic transducer is located on the end of theinstrument to provide an "active" detection system. The ultrasonic waveemitted by the imaging system is detected by the transducer, and anelectrical signal is conveyed back to the imaging system, or thetransducer emits an ultrasonic signal for detection by the imagingsystem. For more general information reference can be made to U.S. Pat.No. 3,556,079 and U.S. Pat. No. 4,249,539. GB-A-2157828 describes aninstrument in which the ultrasonic sensor is connected to a detectioncircuit by a pair of solid conductive paths. This requires quitecomplicated and accurate fabrication techniques.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide an ultrasonicinvasive instrument where the fabrication can be significantly lesscomplicated and therefore less costly.

It has been found unexpectedly that it is not essential to have aconductive or very low resistance, connection to the transducer, butthat satisfactory performance can be made if an ohmic or capacitivecoupling is used.

According to the invention there is provided an ultrasonic invasiveinstrument comprising a device having an ultrasonic sensor secured at ornear a first end of the device which is inserted into the body, and twoelectrically conductive paths extending from the sensor to a second endof the device for connection to the electronic circuitry, the sensorhaving first and second electrode surfaces, at least one of whichsurfaces is electrically connected to a respective conductive path by anohmic or capacitive coupling.

More particularly the invention is applied to a biopsy probe in which anelectrically conductive stylet is arranged to be surrounded by anelectrically conductive cannula. An electrically insulating barrier,such as an electrically non-conducting polymer film is positionedbetween the outer surface of the stylet and the inner surface of thecannula, and the ultrasonic sensor is mounted on the remote end of thestylet and, in use, is electrically coupled by body fluids or the liketo the cannula so that signals generated by the sensor can be detectedby an electronic circuit connected across the near ends of the styletand the cannula.

The electrical connection between the stylet and sensor may be acapacitive and/or an ohmic coupling.

The coupling between the sensor and the needle may be a capacitiveand/or an ohmic coupling, the latter being provided by the mediumpresent in use adjacent the sensor.

Thus the invention provides a construction for an invasive ultrasonicinstrument which is easier to manufacture than the instrument of, forexample, GB-A-2157828.

The invention is applicable to a wide range of instruments used insurgical and medical investigations, diagnosis, treatment and associatedresearch, for example puncture needles, catheters and endoscopes, usedfor example for aspiration of liquids, taking histological andcytological biopsy samples, chorionic villus sampling, umbilical cordblood sampling, amniocentesis, in vivo fertilisation, positioningcapsules for taking small bowel biopsies, ductography, selectivearteriography, phlebography, embolisation, drug administration,radioactive source implantation and cardiac catheterisation.

Other aspects, preferred features and advantages of the invention willbe apparent from the following description and the accompanying claims.

DESCRIPTION OF THE DRAWINGS

The invention will be further described by way of example with referenceto the accompanying drawings, in which:

FIG. 1 shows an ultrasonic invasive instrument forming a firstembodiment of the invention;

FIG. 2 shows an end of the instrument of FIG. 1 on enlarged scale;

FIG. 3 shows a biopsy needle forming a particularly preferred embodimentof the invention; and

FIG. 4 shows another particularly preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, in FIGS. 1 and 2 a metallic stylet 10 has anelectrically insulating outer polymer coating and is surrounded by ahollow metallic cannula or needle 11. A preferred coating is parylene byUnion Carbide which has FDA approval, but other medically approvedcoatings may be used. Alternatively, or as wall, the inner surface ofthe cannula may be coated. An ultrasonic sensor 12 (see FIG. 2) isbonded to the end surface 13 of the stylet 1, or it may be bonded on theside a short way from the end face. The bonding is achieved by a thinlayer 15 of a conventional medically-inert adhesive, but very preferablybiocompatible. The adhesive need not be electrically conductive, sinceit is sufficient to provide an ohmic or capacitive coupling.

The sensor is preferably a PVDF (polyvinylidene difluoride) film, whichis typically 52 microns thick. Other sensors, such as lead zirconatetitanate might be used. Usually, the material has a conductive metalliccoating on its two major surfaces to form electrodes. However, it hasbeen found that it is not necessary to provide these coatings and it isparticularly preferred that uncoated material be used. One advantagewhich this gives is that the uncoated material is transparent and somore easily positioned by eye on the stylet tip. Also, the polarity ofthe connection of the material (i.e. which face is electricallyconnected to which conductor) has been found not to be important.

The solid stylet 10 forms a first conductor and the surrrounding cannula11 forms a second conductor for feeding signals from the sensor 12. Thesensor 12 is electrically coupled to the cannula 11 by body fluids whichwill surround and enter the end of the cannula 11 adjacent the sensor12. In the alternative a conductive fluid, such as saline, may be fedinto the cannula 11, the fluids providing an ohmic or capacitiveelectrical coupling.

An outer sheath 18 and inner core 19 of a co-axial cable 16, which fitson a housing 17, are electrically connected to the near ends of thestylet 10 and the needle 11. The stylet 10 and housing 17 are removeableto allow fluids etc. to be sucked into the cannula 11. A twisted pairtwo-core cable may be used with a surrounding grounded sheath forimproved signal to noise ratio, the wires of the twisted pair beingconnected respectively to the stylet 10 and cannula 11. Signalsgenerated by the transducer 12 are transmitted along the stylet 10 andthe needle 11 to be measured in effect across the near ends of thestylet 10 and the needle 11. The sensor 12 couples electrically with thestylet 10 either ohmically or capacitively, as explained above, and alsocouples with the needle 11 ohmically and/or capacitively. Although thesignals generated by the transducer are small, the apparently poorelectrical connections for the sensor 12 are in fact found to besatisfactory in practice.

The device of FIGS. 1 and 2 is typically for cytological use or a shapedend may be provided on the cannula 11 for histology.

FIG. 3, shows a biopsy needle, the particular design shown being similarto the "Tru-Cut" needle marketed by Travenol Laboratories, Inc. Thestylet 10 has a recess 20 near its end 21. The recess 20 cooperates witha cutting edge 22 on the end of the cannula 11 to take a tissue sampleas the stylet 10 moves back into the cannula 11, as is well known. Theultrasonic sensor may be positioned in the recess 20, but preferably ispositioned on the end surface 23 as in the embodiment of FIGS. 1 and 2.In the recess 20, the sensor is better protected from damage and, inuse, ultrasonic waves impinging on the remote end of the stylet 10 maybe acoustically conducted up the stylet to the sensor at 16. Althoughthis introduces a short acoustic delay, which may cause a registrationerror in the image, this may be clinically insignificant. If requiredthis delay may be corrected for by a suitable signal processing methodin the associated electronic detection and display circuitry. A greaterproblem arises when the probe is positioned in the body with the stylet10 withdrawn into the cannula 11. Body fluids are needed to electricallycouple the sensor 12 to the cannula 11, and these might not penetratepast the end 23. Saline could be injected in the probe to reduce thisdifficulty, but it is particularly preferred that the sensor be mountedon the end surface 23.

The stylet 10 and cannula 11 are electrically connected to themonitoring instrumentation (not shown) by a twisted pair cable 27.

The outer surface of the stylet 10 is electrically insulated from thecannula 11 by a polymer coating. Also, as indicated above, it ispossible to insulate the inner surface of the needle 11 to provide theinsulating barrier between the stylet 10 and the needle 11 or aseparately formed insulating sleeve could also be used in theembodiments of FIGS. 1 and 2 and FIG. 3.

FIG. 4 illustrates another embodiment, in which the probe 30 has ahollow metallic body 31, typically of stainless steel, and a copper wire32 is carried within the hollow core 33. The wire 32 is electricallyinsulated from the body 31 by epoxy resin 34. A PVDF sensor 35 is bondedto the wire 32 by a U-V cured adhesive 36. As before the sensor does notneed a metallic coating on its surface and the adhesive 36 need not beelectrically conductive. The sensor 35 is spaced from the body 31 andits outer surface (electrode) 37 makes electrical contact with the body31 by a capacitive or ohmic coupling, such as by body fluids. A twistedwire pair is connected to the near ends (not shown) of the body 31 andwire 32. The probe 30 may be part of a body tissue sampling device, suchas the device of FIGS. 1 and 2.

Various modifications may be made to the described embodiments and it isdesired to include all such modifications as fall within the scope ofthe accompanying claims.

We claim:
 1. An ultrasonic invasive instrument comprising a devicehaving an ultrasonic sensor secured at or near a first end of the devicefor insertion into the body, and two electrically conductive pathsextending form the sensor to a second end of the device for connectionto electronic circuitry, the sensor having first and second electrodesurfaces, at least one of which surfaces is capable of beingelectrically connected to a said respective conductive path by an ohmicor capacitive conductive fluid.
 2. An instrument as claimed in claim 1,in which the sensor is a PVDF film ultrasonic transducer.
 3. Aninstrument as claimed in claim 2, in which the PVDF is not provided witha metallic coating on one or both of its faces.
 4. An instrument asclaimed in claim 1 in which the sensor is glued in position on thedevice with an electrically non-conducting adhesive.
 5. An instrument asclaimed in any one of claim 1 in which one of the electricallyconductive paths is provided by a wall of the device and, in use, thesensor is ohmically or capacitively coupled to the wall.
 6. Aninstrument as claimed in claim 5, in which the fluidic ohmic orcapacitive conductive fluid is a body fluid.
 7. An instrument as claimedin any one of claims 1 to 6, wherein the sensor is mounted on acylindrical stylet and is electrically coupled to a conductor passingthrough the centre of the stylet, and to the cylindrical stylet wall. 8.An instrument as claimed in any one of claim 1, wherein the sensor ismounted on a stylet which provides a first of the conductive paths andthe second is provided by a cannula surrounding the stylet and throughwhich the stylet moves.